Defense Secretary Chuck Hagel told U.S. troops in Afghanistan on December 7 that their mission was not finished as they shift to a scaled-back role training the Afghan Army.

Speaking at Gamberi base near the eastern city of Jalalabad, Hagel said it was crucial the United States and its partners ensure progress does not get reversed as the U.S.-led force draws down to about 12,500 noncombat troops.

Hagel told a gathering of U.S. and Polish soldiers, "We don't want to see that tremendous progress that's been accomplished...we don't want to see that roll back downhill."

It was Hagel's last visit to Afghanistan as defense secretary after announcing last month that he is stepping down.

From Afghanistan, Hagel flew on to Kuwait.

U.S. President Barack Obama has nominated Ashton Carter, a physicist and former deputy defense chief, to replace Hagel.